💡 Chain Abstraction is in early access.
Chain Abstraction in WalletKit enables users with stablecoins on any network to spend them on-the-fly on a different network. Our Chain Abstraction solution provides a toolkit for wallet developers to integrate this complex functionality using WalletKit. For example, when an app requests a 100 USDC payment on Base network but the user only has USDC on Arbitrum, WalletKit offers methods to detect this mismatch, generate necessary transactions, track the cross-chain transfer, and complete the original transaction after bridging finishes.

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How It Works

Apps need to pass gas as null, while sending a transaction to allow proper gas estimation by the wallet. Refer to this guide for more details.
When sending a transaction, you need to:
  1. Check if the required chain has enough funds to complete the transaction
  2. If not, use the prepare method to generate necessary bridging transactions
  3. Sign routing and initial transaction hashes, prepared by the prepare method
  4. Use execute method to broadcast routing and initial transactions and wait for it to be completed
The following sequence diagram illustrates the complete flow of a chain abstraction operation, from the initial dapp request to the final transaction confirmation

Chain Abstraction Flow

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Methods

The following methods from WalletKit are used in implementing chain abstraction.
💡 Chain abstraction is currently in the early access phase and requires the @ChainAbstractionExperimentalApi annotation.

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Prepare

This method is used to check if chain abstraction is needed. If it is, it will return a PrepareSuccess.Available object with the necessary transactions and funding information. If it is not, it will return a PrepareSuccess.NotRequired object with the original transaction.
Accounts field is a list of CAIP-20 accounts you are sourcing from e.g. Solana account
@ChainAbstractionExperimentalApi
fun prepare(
  initialTransaction: Wallet.Model.InitialTransaction,
  accounts: List<String>,
  onSuccess: (Wallet.Model.PrepareSuccess) -> Unit,
  onError: (Wallet.Model.PrepareError) -> Unit
)

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Execute

This method is used to execute the chain abstraction operation. It broadcasts the bridging and initial transactions and waits for them to be completed. The method returns a ExecuteSuccess object with the transaction hash and receipt. 
@ChainAbstractionExperimentalApi
fun execute(
  prepareAvailable: Wallet.Model.PrepareSuccess.Available,
  prepareSignedTxs: List<Wallet.Model.RouteSig>,
  initSignedTx: String,
  onSuccess: (Wallet.Model.ExecuteSuccess) -> Unit,
  onError: (Wallet.Model.Error) -> Unit
)

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Usage

When sending a transaction, first check if chain abstraction is needed using the prepare method. If it is needed, you must sign all the fulfillment transactions and use the execute method. If the operation is successful, use execute method and await the transaction hash and receipt. If the operation is unsuccessful, send the JsonRpcError to the dapp and display the error to the user. 
    val initialTransaction = Wallet.Model.Transaction(...)
    WalletKit.ChainAbstraction.prepare(
      initialTransaction,
      caip10Accounts,
      onSuccess = { prepareSuccess ->
        when (prepareSuccess) {
          is Wallet.Model.PrepareSuccess.Available -> {
            // If the route is available, present a CA transaction flow

            //sign route transactions
            transactionsDetails?.route?.forEach { route ->
              route.transactionDetails.forEach { transactionDetails ->
                val signedTransaction = Signer.signHash(transactionDetails.transactionHashToSign, EthAccountDelegate.privateKey)
                eip155Signatures.add(signedTransaction)
              }
            }
          }

          //sign initial transaction
          val signedInitialTx = Signer.signHash(transactionsDetails?.initialDetails.transactionHashToSign, EthAccountDelegate.privateKey)
            
            //Call the execute
            WalletKit.ChainAbstraction.execute(prepareSuccess, eip155Signatures, signedInitialTx
                onSuccess = {
                    //The execution of the Chain Abstraction is successfull
                    //Send the response to the Dapp or show to the user
                },
                onError = {
                    //Execute error - wallet should send the JsonRpcError to a dapp for given request and display error to the user
                }
            )
          }

          is Wallet.Model.PrepareSuccess.NotRequired -> {
                  // user does not need to move funds from other chains, sign and broadcast original transaction
          }
        }
      },
      onError = { prepareError ->
            // One of the possible errors: NoRoutesAvailable, InsufficientFunds, InsufficientGasFunds - wallet should send the JsonRpcError to a dapp for given request and display error to the user
      }
   )
For example, check out implementation of chain abstraction in sample wallet with Kotlin.

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Error Handling

When implementing Chain Abstraction, you may encounter different types of errors. Here’s how to handle them effectively:

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Application-Level Errors

These errors (PrepareError) indicate specific issues that need to be addressed and typically require user action:
  • Insufficient Gas Fees: User needs to add more gas tokens to their wallet
  • Malformed Transaction Requests: Transaction parameters are invalid or incomplete
  • Minimum Bridging Amount Not Met: Currently set at $0.60
  • Invalid Token or Network Selection: Selected token or network is not supported
When handling these errors, you should display clear, user-friendly error messages that provide specific guidance on how to resolve the issue. Allow users to modify their transaction parameters and consider implementing validation checks before initiating transactions.

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Retryable Errors

These errors (Result::Err) indicate temporary issues that may be resolved by retrying the operation. Examples of these types of issues include network connection timeouts, TLS negotiation issues, service outages, or other transient errors. For retryable errors, show a generic “oops” message to users and provide a retry button. Log detailed error information to your error tracking service, but avoid displaying technical details to end users.
For errors in the execute() method, a retry may not resolve the issue. In such cases, allow users to cancel the transaction, return them to the application, and let the application initiate a new transaction.

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Critical Errors

Critical errors indicate bugs or implementation issues that should be treated as high-priority incidents: incorrect usage of WalletKit API, wrong data encoding or wrong fields passed to WalletKit, or WalletKit internal bugs.

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Testing

To test Chain Abstraction, you can use the AppKit laboratory and try sending any supported tokens with any chain abstraction supported wallet. You can also use this sample wallet for testing.

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ProGuard rules

If you encounter issues with minification, add the below rules to your application: 
-keepattributes *Annotation*

-keep class com.sun.jna.** { *; }
-keepclassmembers class com.sun.jna.** {
    native <methods>;
    *;
}

-keep class uniffi.** { *; }

# Preserve all public and protected fields and methods
-keepclassmembers class ** {
    public *;
    protected *;
}

-dontwarn uniffi.**
-dontwarn com.sun.jna.**